/*
 * @Author: deng.liu 
 * @Date: 2019-02-19 17:39:02 
 * @Last Modified by: deng.liu
 * @Last Modified time: 2019-02-19 18:05:32
 */
var recLength = 0, recBuffers = [], sampleRate, numChannels;

this.addEventListener('message', function(e) {
    switch (e.data.command) {
        case 'init': 
            init(e.data.config);
            break;
        case 'record': 
            record(e.data.buffer);
            break;
        case 'exportWAV': 
            exportWAV(e.data.type);
            break;
        case 'getBuffer': 
            getBuffer();
            break;
        case 'clear': 
            clear();
            break;
    }
}, false)


function init(config) {
    sampleRate = config.sampleRate;
    numChannels = config.numChannels;
    initBuffers();
}

function clear() {
    recLength = 0;
    recBuffers = [];
    initBuffers();
}

function initBuffers() {
    for (var i = 0; i < numChannels; i++) {
        recBuffers[i] = [];
    }
}

function record(inputBuffer) {
    for (var i = 0; i < numChannels; i++) {
        recBuffers[i].push(inputBuffer[i]);
    }
    recLength += inputBuffer[0].length;
}

function exportWAV(type) {
    var buffers = [];
    for (let i = 0; i < numChannels; i++) {
        buffers.push(mergeBuffers(recBuffers[i], recLength));
    }
    var interleaved;
    if (numChannels === 2) {
        interleaved = interleave(buffers[0], buffers[1]);
    } else {
        interleaved = buffers[0];
    }
    var dataview = encodeWAV(interleaved);
    var audioBlob = new Blob([dataview], { type: type });
    this.postMessage({command: 'exportWAV', data: audioBlob});
}

// 交叉合并左右声道的数据
function interleave(inputL, inputR) {
    var length = inputL.length + inputR.length;
    var result = new Float32Array(length);
    var index = 0, inputIndex = 0;
    while(index < length) {
      result[index++] = inputL[inputIndex];
      result[index++] = inputR[inputIndex];
      inputIndex++;
    }
    return result;
}


// 抹平数组
function mergeBuffers(recordBuffer, recordLength) {
    var result = new Float32Array(recordLength);
    var offset = 0;
    for (var i = 0; i < recordBuffer.length; i++) {
      result.set(recordBuffer[i], offset);
      offset += recordBuffer[i].length;
    }
    return result;

}



function floatTo16BitPCM(output, offset, input) {
    for (let i = 0; i < input.length; i++, offset += 2) {
        let s = Math.max(-1, Math.min(1, input[i]));
        output.setInt16(offset, s < 0 ? s * 0x8000 : s * 0x7FFF, true);
    }
}

function writeString(view, offset, string) {
    for (let i = 0; i < string.length; i++) {
        view.setUint8(offset + i, string.charCodeAt(i));
    }
}

function encodeWAV(samples) {
    var buffer = new ArrayBuffer(44 + samples.length * 2);
    var view = new DataView(buffer);

    /* RIFF identifier */
    writeString(view, 0, 'RIFF');
    /* RIFF chunk length */
    view.setUint32(4, 36 + samples.length * 2, true);
    /* RIFF type */
    writeString(view, 8, 'WAVE');
    /* format chunk identifier */
    writeString(view, 12, 'fmt ');
    /* format chunk length */
    view.setUint32(16, 16, true);
    /* sample format (raw) */
    view.setUint16(20, 1, true);
    /* channel count */
    view.setUint16(22, numChannels, true);
    /* sample rate */
    view.setUint32(24, sampleRate, true);
    /* byte rate (sample rate * block align) */
    view.setUint32(28, sampleRate * 4, true);
    /* block align (channel count * bytes per sample) */
    view.setUint16(32, numChannels * 2, true);
    /* bits per sample */
    view.setUint16(34, 16, true);
    /* data chunk identifier */
    writeString(view, 36, 'data');
    /* data chunk length */
    view.setUint32(40, samples.length * 2, true);

    floatTo16BitPCM(view, 44, samples);

    return view;

}


function getBuffer() {
    var buffers = [];
    for (let i = 0; i < numChannels; i++) {
        buffers.push(mergeBuffers(recBuffers[i], recLength));
    }
    this.postMessage({ command: 'getBuffer', data: buffers });
}